My mother is waiting __ the bus __ line __ the bus stop.

问题描述:

My mother is waiting __ the bus __ line __ the bus stop.

for in on
我妈妈在公交车站排队等车

for,in,at
wait for是固定的词组,等待的意思,后接名次、代词、和动名次.
in line,在队伍中之意.
at指在某地